The present invention relates generally to household appliances and, in particular, to control circuitry for small appliances such as blenders and the like.
Electrical controls for food blenders of the type used for preparation of meals in a kitchen typically include a set of electrical switches or buttons on a front panel that may be used to control the blender motor. Such switches normally provide at least three operating modes: a “pulse” mode in which the blender operates only while a “pulse” button is pressed, an “on” mode in which the blender operates continuously after the “on” button is pressed and until released by pressing of an “off” button, and an “off” mode which cancels the “on” mode when the “off” button is pressed.
These electrical controls may be implemented using “electro-mechanical logic” that employs mechanical features to implement the above mode logic. In such electro-mechanical logic, the pulse button is spring-loaded to return after it is pressed and the on and off buttons are joined with a linkage so that the pressing of the off button releases the on button.
Alternatively, the electrical controls may be implemented using “electronic logic” in which each of the buttons is a momentary contact pushbutton and integrated logic circuitry implements the above modes. An advantage of electronic logic is that it works with low-voltage membrane switches requiring lower actuation forces and providing better sealing against contamination. Electronic logic and low-voltage membrane switches also make it easier to provide feedback using LEDs that can shine through transparent windows in the switch membrane. In contrast, electromechanical logic can result in buttons that are relatively hard to push, require substantial actuation distance, and are hard to seal against environmental contamination.
Low-cost blenders often cannot support electronic logic, principally because of the cost of circuitry necessary to convert 120 VAC power used for the blender motor to regulated, low-voltages required for typical logic circuits, and because of the cost of integrated circuits to implement the logic.